Motor vehicle hydraulic braking systems

ABSTRACT

An hydraulic braking system for motor vehicles comprising a loop circuit around which the hydraulic fluid is pumped when the engine is in operation, to maintain a normal operating pressure in the loop and two branches containing front and rear braking actuators. The brake pedal is linked to a valve in the circuit such that depression of the brake pedal causes a restriction in the loop circuit so as to increase the hydraulic pressure in the system to operate the brakes. The system thus has a normal operating pressure due to circulation of fluid in the loop part of the circuit, and a number of pressure sensitive devices are positioned in various parts of the circuit to detect a fall in the pressure in the part of the circuit with which each is associated and to isolate that part of the circuit from the remainder of the circuit when such a fall in pressure is detected. Thus, in the event of a failure of any part of the circuit at least some of the brakes will still be operable.

United States Patent [191 Peruglia et al.

[ 1 May 29,1973

[541 MOTOR VEHICLE HYDRAULIC BRAKING SYSTEMS Inventors: Marco Peruglia,Turin; Giancarlo Michellone, Cambiano, both of Italy US. Cl ..303/6 C,303/2l F Int. Cl. ..B60t 13/18 Field of Search 303/6 C, 21 F, 84 A;

[56] References Cited UNITED STATES PATENTS 10/1970 Margetts ..303/6 C1/1972 Wellman ...303/6 C X 7/1972 Kish &' Swanson ..303/6 C X 57ABSTRACT An hydraulic braking system for motor vehicles comprising aloop circuit around which the hydraulic fluid is pumped when the engineis in operation, to maintain a normal operating pressure in the loop andtwo branches containing front and rear braking actuators. The brakepedal is linked to a valve in the circuit such that depression of thebrake pedal causes a restriction in the loop circuit so as to increasethe hydraulic pressure in the system to operate the brakes. The systemthus has a normal operating pressure due to circulation of fluid in theloop part of the circuit, and a number of pressure sensitive devices arepositioned in various parts of the circuit to detect a fall in thepressure in the part of the circuit with which each is associated and toisolate that part of the circuit from the remainder of the circuit whensuch a fall in pressure is detected. Thus, in the event of a failure ofany part of the circuit at least some of the brakes will still beoperable.

11 Claims, 2 Drawing Figures Patented May 29, 1973 2 Sheets-Sheet lPatented May 29, 1973 2 Sheets-Sheet 2 MOTOR VEHICLE HYDRAULIC BRAKINGSYSTEMS OBJECTS or THE INVENTION It is one object of the invention toprovide braking circuits which will operate to produce some degree ofbraking in almost any case of failure, whatever the nature of thefailure and at whatever point in the circuit the member which has failedis located.

Another object of the invention is to provide a'braking system of theservo-assisted type in which the servoassistance is produced by thehydraulic braking fluid itself as well as by a fluid of a differentnature circulating in a separate circuit as occurs, for example, insystems fitted with vacuum operated servo devices.

A further object of this invention is to provide a braking system inwhich the hydraulic fluid is subjected to a cooling action in order topromote correct functioning of the braking members even under unusualconditions of use.

SUMMARY OF THE INVENTION According to the present invention, there isprovided an hydraulic braking system for motor vehicles, characterizedin that one part of the circuit is formed as a loop around which thehydraulic fluid can be circulated by a volumetric pump, the loop circuitincluding a reservoir and valve means operable, by a modulator memberlinked to the brake pedal, to restrict the flow of hydraulic fluidaround the said loop circuit to increase the hydraulic pressure tooperate braking actuators in respective branches of the system, therebeing provided atleast one pressure sensitive valve responsive to apressure drop in part of the system to isolate that part of the systemso as to retain sufficient fluid pressure in the remainder of the systemto operate the braking actuators therein.

Preferably the said valve means include a valve shutter slidable in achamber, and resiliently biased by a spring against the action of whichthe shutter is movable by the said modulator member to operate as apiston to increase the pressure of the hydraulic fluid in the saidchamber so as to operate any braking actuators connected thereto if thepump is out of action.

Various other features and advantages of the invention will becomeapparent during the course of the following description, with referenceto the accompanying drawings, which is given purely by way ofnonrestrictive example.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS i 1 switch 50 to a valve device generally indicated 4. Thevalve device 4 is also connected to the tank 1 by means of a pipe 2a soas to define a continuous circulation circuit for the hydraulic fluid.In that branch of the circuit between the volumetric pump 3 and thevalve device 4 there is in addition to the pressure switch 50, a one-wayvalve 6; the pressure switch 50 is operationally connected (by means notshown) to antiskid braking correctors 7 which are linked to the brakingdevices of each wheel, shown diagrammatically in the drawings and marked8 for the front wheels and 9 for the rear wheels. Hydraulic fluid is fedto the rear wheel braking devices via the braking correctors 7 and apipe 10 which leads from the pipe 2 between the volumetric pump 3 andthe pressure switch 50; the front wheel braking devices are fed by meansof a pipe 11 and the associated braking correctors 7, the pipe 11 beingoperatively connected to the valve device 4 via a pair of valves, 12 and13 respectively the operation of which will be described below.

The valve device 4 comprises a cup shaped valve shutter 14 which isslidable in a chamber 16 to one end of which it is resiliently biased bya spring 15. The shutter 14 divides the chamber 16 into two compartmentswhich communicate through an opening 17 formed in an axial extension 17aof the shutter 14. The opening 17 can be closed by a modulator member 5which comprises a pin with one conical end 50 which can be inserted intothe said opening 17 in order to restrict its outlet section, themodulator pin 5 has a fixed collar against which engages a spring 18which extends between the collar of the pin and the bottom of the cupshaped valve shutter 14 to bias the modulator pin away from the opening17.

The valve shutter is shaped so as to define, when it is in the position(illustrated in FIG. 1) to which it is biased by the spring 15 a port 19between the chamber 16 and the pipe 2a communicating with the tank 1. Atthe end of the chamber 16 remote from the modulator 5 there is a valve13 consisting of a shutter which is axially slidable between an openposition (as shown in FIG. 1) and a closed position; both positions aredelimited by snap stops made by engaging a ball catch 20 biased by aspring 21 with corresponding recesses 22 and 23 in the shaft of theshutter of the valve 13.

Movement of the valve shutter 13 from the open to the closed position iscaused by engagement of the end 170 of the pipe 17 which extends fromthe valve shutter 14, when the valve shutter 14 is moved against theaction of the spring 15 by the modulator pin 5.

The valve 12 which lies between the valve device 4 and the pipe 11comprises two valve shutters, a main shutter 24 and a secondary shutter25 which are movable in opposite directions against the actions ofrespective springs 26 and 27 which have different strengths, the spring27 being much weaker than the spring 26.

Referring now to FIG. 1, there is shown a hydraulic fluid tank 1 havinga filler opening sealed by a filler cap la, and a separator baffle lb. Acirculation pipe 2 including a volumetric pump 3 activated by thevehicles engine (not shown) leads from the tank 1 via a pressure Thecircuit described above operates as follows: The brake pedal isconnected to the modulator 5 so that depression of the brake pedalcauses displacement of the modulator 5 so that its conical end 5a,progressively closes the opening 17 thereby increasing the fluidpressure in the lines 2 and 11 due to the operation of the pump3 thusstarting the braking action of both the front .andthe rear wheels. Theincrease in hydraulic pressure is directly related to the restriction ofthe opening 17 by the modulator 5. Progressive closing of the opening 17therefore induces a correspondingly progressive increase in the pressureof the hydraulic circuit in such a way that the pressure is, in fact,boosted. This boosting arises as follows:

As can be seen from the drawing, if the pressure of the fluid in thechamber 16 were caused by movement of the valve shutter 14 acting as apiston, then the pressure P exerted by va force t on the pedal of thebrake if the working cross section of the shutter were A would be givenby:

On the other hand, with the arrangement described above in order toexert the pressure P the force required on the brake pedal, where A isthe cross sectional area of the opening 17, is given by:

This is less than the force t since A is less than A For this purpose itis necessary that the strength of the spring 15 should be much greaterthan the strength of the spring 18 so that when the modulator hascompletely closed the opening 17 the shutter of the valve 14 is heldmore or less immovable by the combination of the spring and thehydraulic pressure in the chamber 16 against any force whatever exertedon the brake pedal. 7 i

If a failure occurs in the pump circuit, then the pressure switch 50operates to cut out all the braking correctors 7. This is most importantsince ifithere is no recirculation of the hydraulic fluid to the tankthe braking correctors would cause an excessive lowering of the oillevel in the tank thereby robbing it ofits safety braking function whichwill be described below.

In other cases of failure the circuit behaves as follows. I I

If the engine stalls, or the volumetric pump 3 fails or the rear wheelbraking circuit ruptures to cause a loss of fluid and a decrease ofpressure in the line 2 then, as mentioned above, all the brakingcorrectors 7 are cut out by the pressure switch 50. I

The lowering of pressure in the pipe 2 between the pump 3 and the valvedevice 4 causes the valve 6 to shut, isolating all that part of thehydraulic circuit containing the pump 3, the pressure switch 50, and therear wheel brakes. The valve shutter 14 assumes the function of a pistonand, urged by the modulator 5 under the action of the brake pedal movesagainst the biasing of the spring 15, to increase the pressure of theoil in the chamber 16. The oil pressure reaches the front wheel brakesvia the valves 13 and 12 to effect braking thereby.

The reserve of oil necessary for the circuit to operate as described isassured by the presence of the baffle platelb in the tank 1. The valve6, apart from the function described above, has the additional functionof preventing the entry of air into the circuit in the case of failureof that branch of the circuit including the volumetric pump 3. With thisobject the valve shutter is biased to the closed position by acompressed spring 6a.

If the front wheel braking circuit fails in any way which causes adecrease in pressure therein this decrease in pressure is transmitted tothe chamber 16 of the valve device 4. In this case the shutter of thevalve I4 is thrust by the modulator 5 against the action of the spring15 until the end 17a of the pipe 17 engages the shutter of the valve 13,which is then urged into the closed position in which it is retained byengagement of the ball catch 20 in the recess 23. The branch 11 of thefront wheel braking circuit is thus completely closed. The rear wheelbraking circuit continues to function normally with servo-assistance dueto the circulation pressure produced by the pump 3. The rear wheelbraking correctors 7 remain operative since the pressure switch 50 iscut in, and the reserve of hydraulic fluid is guaranteed by the baffleplate lb in the tank 1.

If, the front circuit 11 fails at a time when braking is not takingplace the reserve of fluid is preserved by the valve 12 since the spring26 is sufflciently strong to prevent flow of fluid through the valve 12to avoid circuit leakage. On the other hand the spring 27 is such as toallow free return of the fluid after whole circuit braking during normaloperation.

In FIG. 2 there is shown a second embodiment of the invention, which isformed as a system having a double circuit modulator or duplex circuit,and separate circuit branches for the front and the rear wheelrespectively. The parts of the embodiment of FIG. 2 which correspond tointegers of the embodiment of FIG. I will be referred to by the samereference numerals.

Referring now to FIG. 2 it will be seen that the circuit includes areservoir 47 with two baffles 48 and 49 which divide the reservoir 47into three compartments 3 8, 44 and 45. To the compartment 45 of thereservoir there is connected a pipe 46 which leads to a volumetric pump3 driven by the engine (not shown) of the vehicle of which the brakingsystem forms part. Downstream of the pump the pipe 46 branches into twoparts 46a and 46b each of which is connected to respective non-returnvalves 39 and 34 and thence to a valve device 4. The valve device 4comprises a cylinder in which there are two slidable valve shutters 14and 51, respectively biased by springs 15 and 61.

The shutter 51 separates two chambers, 35 and 40 within the cylinder andhas a port 62 through which the chambers 35 and 40 can communicate. Theshutter 14 is similar to the shutter 14 described with reference to FIG.1 and divides, in its turn, two chambers which communicate through atubular port 17 of the shutter 14.

The chamber 35 is connected to the pipe 46b and also to the pipe 11 forfeeding hydraulic fluid to the braking correctors 7 and thence to thebrakes 8 of the front wheels. Additionally, the chamber 35 communicateswith the compartment 38 of the reservoir 47 through a valve 52 and apipe 37; the shutter of the valve 52 is operated by a cam ridge 63 inthe shutter 51. Similarly the pipe 46a is connected to the chamber 40 towhich is also connected the pipe 10 for feeding hydraulic fluid to thebraking correctors 7 of the rear wheels and thence to the brakes 9; apipe 43 leads from a port 42 to connect the chamber 40 with thecompartment 44 of the reservoir.

The valve shutters l4 and 51 are both operated by the modulator member 5which is formed as a pin having a first part terminating in afrusto-conical end 5a for controlling the port 17, an intermediate shaft5b, and

' a terminal head 5c for controlling the communication port 62 betweenthe two chambers 35 and 40. A pressure switch 50 which is operativelyconnected to the braking correctors 7 is located on the pipe 46downstream of the pump 3.

The operation of the embodiment of FIG. 2 is as follows:

Under normal conditions, when the brake pedal, which is linked to themodulator member 5, is not depressed, the volumetric pump 3 causes thehydraulic fluid to circulate through both the front and rear hydrauliccirculation circuits; the front circuit comprises action of the spring61 which causes closure of the shutter of the valve 52. The progressiveclosing of the port 17 induces a progressive increase of pressure in thecircuit which is therefore modulated as described with reference to FIG.1.

-Rupture of that part of the hydraulic circuit which includes the pumpinduces a loss of servo-assistance and exclusion of the brakingcorrectors 7 as described in relation to FIG. 1, but partial braking mayoccur for both the front and the rear braking circuits due to the actionof the piston formed by the shutters l4 and 51 in a manner similar tothat described with reference to FIG. 1; adequate oil reserve beingensured by the fact that the reservoir 47 is divided into separatecompartments. In this case both valves 34 and 39 operate to isolate thepart of the circuit containing the pump 3 from the remainder of thecircuit.

Similarly, a rupture in either the front or rear braking circuit willcause loss of servo-assistance and cutting out of the braking correctorsthrough the entire hydraulic circuit which will, nevertheless, be ableto perform braking operation due to the aforesaid piston function of thecorresponding shutter 14 or 51 and to the presence of the correspondingreserve tank which ensures a supply of the hydraulic fluid. For example,if the pressure in the front wheel braking circuit falls the pressureswitch 50 will operate to cut out the braking correctors 7 and thepressure difference between the chambers 35 and 40 will cause the valveshutter 14 when moved by the modulator 5 to move the shutter 51 to aposition where the valve 52 is closed. Following this further depressionof the modulator 5 under the action of the brake pedal, causes the valveshutter 14 to .act as a piston to operate the rear wheel brakes 9. On

the other hand, a fall in the pressure of the rear wheel braking circuitwill cause the shutter 14 to approach the shutter 51 when moved by themodulator 5 until the enlarged end 5c abuts the shutter 51 to form amechanical connection so that the shutter 51 is moved as apiston by themodulator 5 to operate the front wheel said brake means to said theimprovement wherein:

said circuit means is formed as a loop part including said reservoirmeans and said brake pedal means, and at least first and second branchparts containing said brake means,

pump means operative to circulate hydraulic fluid around said loop partof said circuit means, said brake pedal means operating, when said brakepedal is depressed, to restrict the flow of hydraulic fluid in said looppart of said circuit means to increase the hydraulic pressure in saidsystem to operate said brake means, and

pressure sensitive valve means in said system, said pressure sensitivevalve means operating to iso' late part of said circuit means when itdetects a drop in pressure therein whereby sufficient hydraulic pressureis retained in the remainder of said circuit means to operate said brakemeans therein.

2. The hydraulic braking system of claim 1 wherein said brake pedalmeans includes a valve connected to a brake pedal, said valve comprisinga first valve shutter slidable in a bore in the valve body,

spring means biasing said first valve shutter in a first direction alongsaid bore,

said valve shutter being movable along said bore in a direction oppositesaid first direction if said pump means is out of action, to increasethe pressure in said system to operate said brake means therein.

3. The hydraulic system of claim 2 wherein said first valve shutter iscup shaped and positioned in said bore in said valve body such as toseparate said bore into two chambers,

an opening in said valve shutter, said two chambers of said bore in saidvalve body communicating through said opening in said valve shutter,

modulator means connected to said brake pedal means, said modulatormeans operating to control the size of said opening in said valveshutter in dependence on the position of said brake pedal means.

4. The hydraulic system of claim 3 wherein said first valve shutter isprovided with an axial extension, said opening in said valve shutterbeing formed as a bore through said axial extension,

a second valve shutter in said bore in said valve body, said secondvalve shutter controlling communication between said loop part of saidcircuit means and said first branch of said circuit means containingsaid brake means of said front wheels,

said first valve shutter being movable against the action of saidbiasing spring means to move said second valve shutter to a closedposition when the pressure in said first branch of said circuit falls.

5. The hydraulic system of claim 1 wherein there is a non-return valvemeans in said loop part of said circuit upstream of said brake pedalmeans, said nonreturn valve means operating to prevent any flow ofhydraulic fluid in said loop part of the circuit in a direction oppositethe normal circulation direction.

6. The hydraulic system of claim 1 including:

further valve means between said brake pedal means and said first branchof said circuit, said further valve means having two valve shutters,

spring biasing means biasing said two valve shutters in respectiveopposite directions,

said further valve means operating to prevent a flow of hydraulic fluidto said first branch of said circuit in the event of a failure leadingto a loss of pressure in said first branch, and to allow such flow undernormal operating conditions.

7. The hydraulic system of claim 1 wherein said loop circuit meansincludes a pressure sensitive switch,

braking correctors in said first and second branches of said circuit,

means operatively connecting said pressure sensitive switch to saidbraking correctors, said pressure sensitive switch operating to preventsaid braking correctors from operating when it detects a fall inpressure in said loop circuit.

8. The hydraulic system of claim 1 wherein said reservoir means includesat least one baffle plate means forming at least one reserve tank withinsaid reservoir means, and

means connecting said reserve tank directly to said brake pedal means.

9. The hydraulic system of claim 1 wherein said loop part of saidcircuit has two branches downstream from said pump means,

respective non-return valve means separately connecting each said loopcircuit branch to said brake pedal means,

first and second valve shutters separately slidable in a common bore inthe valve body of said brake pedal means,

said,first and second valve shutters respectively controlling theconnection of said first and second branches of said circuit means tosaid first and second branches of said loop circuit means.

10. The hydraulic system of claim 9 wherein said first valve shutterseparates said bore in said valve body into first and second chambers,

an opening in said first valve shutter, said first and second chamberscommunicating through said opening in said first shutter and formingpart of said first branch of said loop circuit,

said second valve shutter separating said bore in said valve body intothird and fourth chambers,

an opening in said second valve shutter, said third and fourth chamberscommunicating through said opening in said second valve shutter andforming part of said second branch of said loop circuit.

11. The hydraulic system of claim 10 wherein said brake pedal meansincludes a modulator member operatively connecting said brake pedal andsaid first and second valve shutters, said modulator member comprising afirst part having a frusto-conical face cooperating with said opening insaid first valve shutter to control fluid flow therethrough and a secondpart having an enlarged end cooperating with said opening in said secondvalve shutter to control fluid flow therethrough.

1. In a hydraulic braking system for motor vehicles, of the typecomprising: reservoir means containing said hydraulic fluid, brake meansassociated with each wheel of the vehicle, circuit means connecting saidbrake means to said reservoir, and brake pedal means operable toincrease the pressure in said circuit means to operate said brake means,the improvement wherein: said circuit means is formed as a loop partincluding said reservoir means and said brake pedal means, and at leastfirst and second branch parts containing said brake means, pump meansoperative to circulate hydraulic fluid around said loop part of saidcircuit means, said brake pedal means operating, when said brake pedalis depressed, to restrict the flow of hydraulic fluid in said loop partof said circuit means to increase the hydraulic pressure in said systemto operate said brake means, and pressure sensitive valve means in saidsystem, said pressure sensitive valve means operating to isolate part ofsaid circuit means when it detects a drop in pressure therein wherebysufficient hydraulic pressure is retained in the remainder of saidcircuit means to operate said brake means therein.
 2. The hydraulicbraking system of claim 1 wherein said brake pedal means includes avalve connected to a brake pedal, said valve comprising a first valveshutter slidable in a bore in the valve body, spring means biasing saidfirst valve shutter in a first direction along said bore, said valveshutter being movable along said bore in a direction opposite said firstdirection if said pump means is out of action, to increase the pressurein said system to operate said brake means therein.
 3. The hydraulicsystem of claim 2 wherein said first valve shutter is cup shaped andpositioned in said bore in said valve body such as to separate said boreinto two chambers, an opening in said valve shutter, said two chambersof said bore in said valve body communicating through said opening insaid valve shutter, modulator means connected to said brake pedal means,said modulator mEans operating to control the size of said opening insaid valve shutter in dependence on the position of said brake pedalmeans.
 4. The hydraulic system of claim 3 wherein said first valveshutter is provided with an axial extension, said opening in said valveshutter being formed as a bore through said axial extension, a secondvalve shutter in said bore in said valve body, said second valve shuttercontrolling communication between said loop part of said circuit meansand said first branch of said circuit means containing said brake meansof said front wheels, said first valve shutter being movable against theaction of said biasing spring means to move said second valve shutter toa closed position when the pressure in said first branch of said circuitfalls.
 5. The hydraulic system of claim 1 wherein there is a non-returnvalve means in said loop part of said circuit upstream of said brakepedal means, said non-return valve means operating to prevent any flowof hydraulic fluid in said loop part of the circuit in a directionopposite the normal circulation direction.
 6. The hydraulic system ofclaim 1 including: further valve means between said brake pedal meansand said first branch of said circuit, said further valve means havingtwo valve shutters, spring biasing means biasing said two valve shuttersin respective opposite directions, said further valve means operating toprevent a flow of hydraulic fluid to said first branch of said circuitin the event of a failure leading to a loss of pressure in said firstbranch, and to allow such flow under normal operating conditions.
 7. Thehydraulic system of claim 1 wherein said loop circuit means includes apressure sensitive switch, braking correctors in said first and secondbranches of said circuit, means operatively connecting said pressuresensitive switch to said braking correctors, said pressure sensitiveswitch operating to prevent said braking correctors from operating whenit detects a fall in pressure in said loop circuit.
 8. The hydraulicsystem of claim 1 wherein said reservoir means includes at least onebaffle plate means forming at least one reserve tank within saidreservoir means, and means connecting said reserve tank directly to saidbrake pedal means.
 9. The hydraulic system of claim 1 wherein said looppart of said circuit has two branches downstream from said pump means,respective non-return valve means separately connecting each said loopcircuit branch to said brake pedal means, first and second valveshutters separately slidable in a common bore in the valve body of saidbrake pedal means, said first and second valve shutters respectivelycontrolling the connection of said first and second branches of saidcircuit means to said first and second branches of said loop circuitmeans.
 10. The hydraulic system of claim 9 wherein said first valveshutter separates said bore in said valve body into first and secondchambers, an opening in said first valve shutter, said first and secondchambers communicating through said opening in said first shutter andforming part of said first branch of said loop circuit, said secondvalve shutter separating said bore in said valve body into third andfourth chambers, an opening in said second valve shutter, said third andfourth chambers communicating through said opening in said second valveshutter and forming part of said second branch of said loop circuit. 11.The hydraulic system of claim 10 wherein said brake pedal means includesa modulator member operatively connecting said brake pedal and saidfirst and second valve shutters, said modulator member comprising afirst part having a frusto-conical face cooperating with said opening insaid first valve shutter to control fluid flow therethrough and a secondpart having an enlarged end cooperating with said opening in said secondvalve shutter to control fluid flow therethrough.